Proposal of demolished concrete recycling system based on performance evaluation of inorganic building materials manufactured from waste concrete powder

The rapid industrial development and global population growth of the past century have resulted in an exponential increase of resource consumption and thus caused elevated CO₂ emissions that, in turn, are held responsible for global warming and associated environmental problems that require urgent solutions. Specifically, increase of cement production causes CO₂ pollution and generates a significant amount of concrete waste. Waste concrete, the major component of construction waste, can be efficiently recycled and is mainly used as a roadbed or backfill material. However, as no further resource recycling is expected for waste concrete, more efficient and productive recycling systems are sought after. Herein, waste concrete powder is used to produce added-value inorganic building materials, namely recycled cement and solidification. The characteristics of recycled cement (manufactured through calcination) are evaluated in terms of free lime content, mineral composition, density, color, flow test and strength, and the performance of recycled cement is found to be identical to that of ordinary Portland cement. X-ray diffraction and compressive strength analyses of the solidification manufactured through hydrothermal synthesis show that blocks of the desired strengths can be produced by adjusting the degree of consolidation and curing conditions. Based on these results, this study proposes a concrete waste recycling system to reduce the amount of construction waste and prevent resource depletion.